Heat Transmission

1
Heat Transmission

• HVAC 6c
• CNST 305
• Environmental Systems 1
• Dr. Berryman

2
Temperature Gradients

• The temperature differential between two separate
  surfaces as heat transmits across them.
• A Proportional calculation
• Uses IA OA Temperatures
• R values
• Purpose
• Determine surface temperatures
• MRT
• Dew Point

3
Develop Thermal Resistant Values
Note This is an actual construction in Grand
Island
Wall Section
4
Determine Design Temperatures (winter)
Lincoln, NE
OA 5oF
IA 75oF
?t 80oF
5
Calculate Gradients
Lincoln, NE
OA 5oF
IA 75oF
OA Air film
80oF x
0.6 oF
AL Siding
And so forth
80oF x
2.3 oF
R19 Batt
71.1 oF
?t 80oF
6
Surface Temperatures
Lincoln, NE
OA 5oF
IA 75oF
72.7oF
75oF 2.3
?t 80oF
7
Surface Temps (cont.)
Lincoln, NE
OA 5oF
IA 75oF
71.5oF
75oF (2.31.2)
?t 80oF
8
Surface Temps (cont.)
Lincoln, NE
OA 5oF
IA 75oF
0.4oF
75oF(2.31.271.1)
?t 80oF
9
Heat Transmission
Lincoln, NE
Temperature
IA 75oF
OA 5oF
10
Application?

• Scenario
• You have been called in as a consultant to find
  out why a certain building is having the
  following problems
• On the south side of the building, the sheathing
  is warping between studs
• Same sideAL siding is popping loose
• During the winter they occupants cannot keep the
  building any warmer than 65oF (in fact, some
  liquid items near the north facing wall have
  froze)
• Also, at different point of time in the winter,
  all of the insulated double pane glass has
  frosted over on the inside
• Snow has accumulated on the inside during heavy
  blustery snow storms
• High electric bills for heating and cooling

Case Study
11
At inspection, you see
Siding pulled away
North Side
Siding warps
12
You see
Siding warps in and out every 16
South Side
13
You see
You note that the snow extends into the closet
North Side Windows
14
Wall inspection

• Nothing behind AL siding but bare OSB sheathing
• R19 batt insulation not properly installed
• mmhhh..

Request Blower Door Test
15
Blower Door Test

• A blower door is a large calibrated fan that is
  temporarily mounted in a house door to measure
  the "leakiness" of the house
• Smoke puffer
• Infrared camera
• Calculate room air change

A recreation of a 20 mph wind
16
You discover

• Air leaks
• Around doors and windows
• Behind plumbing fixtures
• Between sill plate and floor
• Infrared
• Shows air infiltrating around each insulation
  batt and at sill plate
• Calculations from pressure differentials
• 133 CFM infiltration (ASHRAE recommends 10 cfm
  for residential)
• 35 CFM ventilation

17
Your Notes after Inspection

• Heating/Cooling sized correctly
• You sketch the wall construction
• Determine R values
• Wall
• Window
• IA conditions DB75oF WB 56oF
• Calculation winter surface wall temps

18
?
What next?
19
Check for condensation w/in walls
Vapor Barries on Warm Side of Construction
20
Check Windows
OA Air Film
IA DB75oF WB 56oF
DS Glass
Seal Windows/Doors
Air Space
Inside Surface Temperature?
DS Glass
48oF
IA Air Film
W/30 RH DP39oF
What about 40 or 50 RH
?t 80oF
21
Next Time

• Heat Gains
• Chapter 2.6 2.8 (Toa)